The invention relates to a spatially resolving range-finding system for constructing three-dimensional objects. Such systems are preferably used to identify persons or objects for the purpose of access control or for general surveillance tasks. Sensor systems which record and process in three dimensions are becoming increasingly important for the most varied tasks in industrial technology. The conceivable applications are extremely manifold and comprehensive and must be supported by a new generation of optical sensors for industrial metrology.
Known optical radar systems, such as laser radar, for example, are based either on the principle of laser pulse travel time measurement or on the determination of the phase indifference of modulated laser light for the purpose of deriving the object distance. Mechanical scanning devices are additionally required for the purpose of constructing a three-dimensional imaging system. This leads to a relatively expensive electronic and mechanical outlay which restricts the use of such three dimensional systems to a few special applications.
Also known are methods in which depth photos are obtained (gated view) with the aid of short term laser illumination and electrooptic switches as well as with CCD cameras. Disadvantages of these sensors reside in a high laser power and in expensive electrooptic shutters. Since CCD cameras generally are operated only according to the television standard, only long read out times can be achieved.
It is the object of the invention to provide, by avoiding the disadvantages of the prior art, a spatially resolving range-finding system with the aid of which it is possible to generate three-dimensional images rapidly and cost-effectively.
This object is achieved by means of the combination of features corresponding to claim 1.
A substantial feature of the invention resides in executing the implementation of the range-finding system using only solid state technology. Furthermore, an single relatively strong light source is replaced by an arrangement, for example in the form of a matrix, of weaker light sources. The light power in relation to the previously high power of a single light source is reduced in relation to the whole-area illumination relative to the number of pixels. The range-finding system manages without moving parts. Limits of laser protection regulations can be observed straight away. Owing to the corresponding arrangement of light sources, on the one hand, and receiving elements of a solid state image converter, on the other hand, it is possible for the object points illuminated by a light source and thereby defined to be respectively received with accurate assignment by a receiving element of the solid state image converter and evaluated with regard to the range.
The distribution of a relatively high light power over a multiplicity of light sources with a prescribed arrangement produces advantages such as a shorter rise time of the amplitude of the light, a higher accuracy of the measurement and ease of compliance with limits, for example from laser protection regulations.
The range-finding system resolves pixels such that individual object points or their range or their contour value can be imaged in a differentiated fashion. This is achieved, in particular, by an advantageous configuration in which the system is provided with light sources which can be driven by random access and receiving elements which can be read out by random access. The correspondence between light sources and receiving elements can advantageously be varied in such a way that not only is there a 1:1 assignment, but, for example, one light source may correspond to several receiving elements combined to form one group. Equally, a group of light sources can serve a single receiving element.
The result of a measurement consists in a generated three-dimensional image of an object, a contour image, or in the form of a sectional view which reproduces the external shape of the object at a specific section of the object with the aid of the illuminating beams.
A whole-area illumination of an object is expediently performed with the aid of a whole-area arrangement with respectively dedicated light sources and receiving elements. It is advantageous for these arrangements respectively to be designed rectangularly in the form of a matrix. If there is no need for such a whole-area illumination or measurement of an object, the light sources and the receiving elements can be arranged in a fashion matched to the task. This means, for example, that, while retaining the correspondence between light sources and receiving elements, a specific line or surface is selected in each case as their arrangement, a corresponding line or surface on the object being detected. Designing this arrangement in a fashion matched to the task is taken to mean that the corresponding arrangements of the light source and the receiving elements are adapted to the shape of the object or to probable positions of the object.
It is advantageous to use modulable laser diodes as light sources. The design of the solid state image converter in the form of an CMOS (metal oxide semiconductor) image converter is associated with a cost-effective design which permits individual receiving elements to be read out by random access in a rapid and reliable fashion.
The use of a spatially resolving range-finding system according to the invention for the purpose of building entrance safeguarding is associated with particular advantages. An appropriate sensor operates with light and not with other, potentially damaging radiations. If laser diodes are used, their individual light power is so low that laser protection regulations are complied with straight away. The arrangement or configuration of the transmitting and receiving units of the measuring system can be adapted specifically to the object.